To Cover
To Hide, To Lay Upside Down, To Turn Over
transitive verb, ichidan verb
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means bow or lay, so the verb version is what when you try to cover or to hide something. You're doing the action to something, you're not the one hiding.
ふせる
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
Who's that you're trying to cover up? It's your fool (ふ) brother. He keeps doing embarrassing things and trying to get you in trouble. So you're trying to hide him with your jacket. Well we see him, we know he's a fool, so you can stop now.
どうして弟が犯罪者であることを伏せていたんだ。
Why would I cover up my younger brother being a criminal?